The properties of visual pigments (human rhodopsin, midshipman rhodopsin, the gecko 521-pigment, chicken iodopsin and other selected ones will be investigated and compared. This will include examination of these pigments in situ as well as in solution. The properties to be examined include their thermal behavior, their photosensitivity, the meta-III intermediate, the effects of pH and other ions (chloride and nitrate), their stereospecificity, and the parameters involved in the spontaneous regeneration that occurs following specific bleaches. In the experimental procedures agents such as NH2OH, Na2BH4, p-mercuribenzoate, dithiothreitol and diverse retinal and 3-dehydroretinal isomers, as well as analogues thereof, will be employed. A search will also be made for pathological human eyes, such as eyes of persons with retinitis pigmentosa, in order to examine the rhodopsin for any deviations from the normal properties. Behind these examinations lie ideas involving a possible isomerase action of opsin following a photic bleach, the possible role of the metarhodopsin-III in human vision, and the biological interpretation of the gecko visual pigments as components of cells in phylogenetic transmutation.